linux-kernel - [PATCH 0/2] mm/uffd: Fix vma merge/split

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Date:   Wed, 17 May 2023 11:04:06 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Lorenzo Stoakes <lstoakes@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Rapoport <rppt@...nel.org>, peterx@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: [PATCH 0/2] mm/uffd: Fix vma merge/split

This series contains two patches that fix vma merge/split for userfaultfd
on two separate issues.  The patchset is based on akpm/mm-hotfixes-unstable
with 2f628010799e reverted (where patch 1 should be used to replace it
which seems to be the plan we reached).

The major changes comparing to the patches I attached to the reply:

  - Fixed up patch 1 on vma_prev() side effect pointed out by Liam, further
    I simplified it to just bring back the two lines missing, so even shorter.

  - Add fixes tags for both patches, I decided to copy stable for both
    patch in this version, even though patch 2 is more or less tentative
    (as I don't see anything wrong besides vma didn't trigger a merge).

Patch 1 fixes a regression since 6.1+ due to something we overlooked when
converting to maple tree apis.  The plan is we use patch 1 to replace the
commit "2f628010799e (mm: userfaultfd: avoid passing an invalid range to
vma_merge())" in mm-hostfixes-unstable tree if possible, so as to bring
uffd vma operations back aligned with the rest code again.

Patch 2 fixes a long standing issue that vma can be left unmerged even if
we can for either uffd register or unregister.

Many thanks to Lorenzo on either noticing this issue from the assert
movement patch, looking at this problem, and also provided a reproducer on
the unmerged vma issue [1].

Please have a look, thanks.

[1] https://gist.github.com/lorenzo-stoakes/a11a10f5f479e7a977fc456331266e0e

Peter Xu (2):
  mm/uffd: Fix vma operation where start addr cuts part of vma
  mm/uffd: Allow vma to merge as much as possible

 fs/userfaultfd.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

-- 
2.39.1